Existing methods for reducing backlash in a gear train typically involve pre-loading the internal members of the gear train. One method uses a flexible member to apply a torque between the two halves of a split gear to maintain uninterrupted engagement between corresponding teeth on the two halves of the split gear and opposite sides of the neighboring teeth of the gear being engaged.
Another method uses a flexible member to apply a torque between two carriers, each of which are rotatably coupled to one half of a split gear. The associated torque maintains uninterrupted engagement between corresponding teeth on the two halves of the split gear and opposite sides of the teeth of the gear being engaged.
Another method uses a flexible member to apply a radial force to a gear which is slidably coupled to a carrier along a radial axis. The associated force maintains uninterrupted engagement between both sides of the teeth of the gear and the gear being engaged.
Another method uses a gear with split, flexible teeth that are tangentially compressed when engaged to maintain uninterrupted engagement between the two halves of the split gear teeth and neighboring teeth on the gear being engaged.
Each pre-loading method introduces a static force which is present regardless of the external load applied to the gear train. This internal force generates friction and reduces energy efficiency under all but the maximum rated loading condition. If the external applied torque exceeds the internal preload torque, the flexible members comply and backlash returns. Consequently, the choice of spring constant trades off energy efficiency with output shaft stiffness, or torque capacity.
Anti-backlash reducer gears may be used to provide uninterrupted engagement between a sun gear and an orbit gear, thereby resulting in an anti-backlash planetary gear. Planetary gears have a number of advantageous qualities and are found in a variety of configurations. One configuration comprises a sun gear, an orbit gear, and one or more planet pinion gears mounted on a carrier. The orbit gear is the reference, the sun gear is the input, and the carrier is the output. The reducer gears may be conventional or stepped pinion gears.
Another configuration comprises two sun gears and one or more planet pinion gears mounted on a carrier. One sun gear is the reference, the carrier is the input, and the other sun gear is the output. The reducer gears may parallel or angled with respect to the sun gears. When the reducer gears are parallel, they are stepped pinion gears. When the reducer gears are angled, they may be conventional or stepped pinion gears.
Another configuration comprises two orbit gears and one or more planet pinion gears mounted on a carrier. One orbit gear is the reference, the carrier is the input, and the other orbit gear is the output. This configuration is commonly referred to as an orbit gear and is capable of higher reduction ratios than a conventional planetary gear.
Another configuration comprises two sun gears and one stepped ring gear mounted on a carrier. One sun gear is the reference, the carrier is the input, and the other sun gear is the output. This configuration is an alternate version of an orbit gear.
Another configuration comprises a reference gear, an output gear and a stepped gear mounted on a carrier. The stepped gear is angled with respect to the reference and output gears and follows a nutating path. This configuration is commonly referred to as a nutating gear and is capable of higher reduction ratios than a conventional planetary gear.
Another configuration is similar in construction to a planetary gear but the carrier is the reference and the orbit is the output. This configuration is commonly referred to as a star gear and is capable of lower reduction ratios than a conventional planetary gear but may be more energy efficient at high speeds since the stationary carrier does not experience mechanical resistance from the internal lubricant.
The exemplary embodiments disclosed herein each comprise one or more pairs of reducer assemblies to provide a low backlash coupling between a drive and driven gear without any internal pre-load forces. A backlash reduction method biases the two reducer assemblies in each pair in opposite directions to provide a stiff, low backlash, engagement path between the drive gear and driven gear for both directions of rotation. No energy is lost to pre-loading friction and the engagement paths do not comply under heavy loads. No flexible members or adjustment mechanisms are required and the method may be used to compensate for wear.